Forced air cooled radioactive materials container

ABSTRACT

An improved radioactive materials container system having a system of ducts and nozzles for efficient forced air cooling of a finned radioactive materials container.

United States Fateni Carrel W. Smitli San Jose, Calil.

Jan. 24, 1969 Nov. 9, 1971 General Electric Company Inventor Appl. No. Filed Patented Assignee FORCED AIR COOLED RADIOACTIVE MATERIALS CONTAINER 2 Claims, 18 Drawing Figs.

10.8. Cl 2511/1108, 250/106 llnLCl (HMS/00 Field of Search 250/ 1 06, 108 WS [56] References Cited UNITED STATES PATENTS 3,111,586 11/1963 Rogers 1. 250/108 3,391,280 7/1968 Bonilla et a1 250/108 3,483,381 12/1969 Bonilla et a1 250/108 Primary Examiner-Archie R. Borchelt Attorneys-Ivor J. James, Jr., Samuel E. Turner, John R.

Duncan, Frank L. Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: An improved radioactive materials container system having a system of ducts and nozzles for efficient forced air cooling of a finned radioactive materials container.

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FORCED AIR COOLED RADIOACTIVE MATERIALS CONTAINER BACKGROUND OF THE INVENTHON Nuclear chain fission reactions and the reactors in which they take place are now well-known. A typical reactor in-- cludes a chain reacting assembly or core made-up of nuclear fuel material contained in fuel elements. The fuel material is generally encased in a plurality of corrosion-resistant heat conductive tubes or cladding. A plurality of these fuel rods are secured together in a fuels subassembly or bundle. The reactor core, made-up of a plurality of these subassemblies or bundles is enclosed in a container through which the reactor coolant flows. As the coolant passes between the spaced fuel rods, it is heated by energy given off during the fission reaction in the fuel material. The heated coolant then leaves the reactor, the heat energy is used to perform useful work, such as by driving a turbine-generator set, and the now-cooled coolant is recycled back to the reactor.

The nuclear fuel material contains fissionable atoms such as U-233, U-235, Pu-239 and Pu-24l. The fuel may be in ele mental or compound form. When the nucleus of such an atom absorbs a neutron, a nuclear fission frequently occurs. This produces on the average two fission product atoms of lower atomic weight, several high energy neutrons and a large amount of kinetic energy. The kinetic energy of the fission products and fission neutrons is quickly dissipated, producing heat. So long as at least one neutron from each fission event induces a subsequent fission event, the fission reaction is selfsustaining. The fissionable atoms are thus gradually consumed. Some of the fission products produced are strong neutron absorbers (neutron poisons) which absorb neutrons which would otherwise contribute to the chain reaction. The fission reaction, therefore, tends to decrease and cannot be maintained indefinitely on a given level.

In some nuclear reactors, fertile materials such as U-238 may be included in the fuel elements in addition to the fissionable material. During the fission reaction, the fertile material, e.g., U-238, is irradiated with neutrons which convert a part of the U-238 to the fissionable isotope, f u-239. The concentration of Pu-239 in the fuel gradually rises with irradiation and reaches an equilibrium value. The Pia-2.39 atoms fission similarly to the original U-235 fuel, thus contributing to the maintenance of the chain reaction.

Except in the breeder-converter type of reactor, the quantity of fissionable material created by fertile atom conversion is always less than the rate at which the original fissionable atom quantity is consumed. Ultimately, the operating power level of the reactor decreases to the point at which the reactor must be shut down for refueling. At least a suitable fraction of the irradiated fuel assemblies are removed and replaced with new fuel having the desired concentration of fissionable atoms and no fission product neutron poisons. The reactivity of the refueled core is thus increased to the extend necessary so that the desired power level can be maintained.

The irradiated reactor fuel removed from the reactor contains a valuable quantity of the original fissionable material. In addition, the irradiated fuel contains a significant quantity of fertile material, and of fissionable material converted from fertile material. Also, certain fission product and/or transuranic isotopes of considerable value may be contained in the fuel. Therefore, it is highly desirable that the irradiated fuel material be reprocessed to recover and separate these materials for reuse.

Large chemical reprocessing plants are being constructed to reprocess this fuel. Since various safety requirements, such as requirements for shielding and economic factors, increase very little as the size of a plant is increased, very large centrally located fuel recovery plants are most economical to operate. Thus, it is generally necessary to ship the irradiated nuclear reactor fuel material substantial distances from the reactors to the reprocessing plants. The irradiated fuel material contains many highly radioactive fission product isotopes,

such as Sr-90, Cs-l 37 and Ce-l44. Also, considerable heat is produced in the irradiated fuel by the decay of the radioactive fission product isotopes. Thus, there are very stringent requirements on the shipping containers to assure the public safety along the route of shipment of the irradiated fuel materials. Similar shipping requirements, of course, exist where highly radioactive material other than irradiated nuclear reactor fuel is being shipped long distances.

In addition to radiation shielding to protect the public from the normal radioactivity in the material, the container must physically retain fission products (solids and gases) present in the fuel. The container should retain essentially all of the nonvolatile radioactive materials and release only a limited quantity of the gases even in the event of severe overheating such as might occur if the container were involved in a fire. It is important that the container not severely rupture should this over heating continue for a significant time. Similarly, the container must be resistant to severe impact such as might occur in a highway accident or railroad derailment. One of the most important characteristics of a radioactive material shipping container is its ability to dissipate the heat produced by decay of the radioactive isotopes. While it is possible to cool the container by natural convection, this requires that the quantity of radioactive material in the container be so small as to be uneconomical for irradiated power reactor fuels. Containers have been designed using closed loop cooling systems in which a liquid coolant is piped through the container and then to a secondary heat exchanger which radiates the heat to the atmosphere. These systems, however, require complex controls, piping, and heat exchangers. The penetrations into the container body are a safety hazard since they weaken the container and increase the chances of leakage. Also, the properties of a liquid coolant may vary with temperature. For example, if the liquid is water, it may freeze at very low temperatures and may evaporate at high temperatures. It is possible to decrease the quantity of heat produced by isotopic-decay by holding the fuel after removal from a nuclear reactor for a long period of. time before shipping. However, since many months delay is required to produce a significant decrease in the heat output of the irradiated fuel, it is uneconomical to maintain large quantities of expensive fuel in inventory for long periods.

Thus, there is a continuing need for improved containers for shipping irradiated nuclear reactor fuel material and other highly radioactive materials which provide improved reliability, safety and capacity.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a shipping container for radioactive materials which overcomes the above-noted problems.

Another object of this invention is to provide a radioactive materials shipping container having improved heat dissipation characteristics.

Another object of this invention is to provide a shipping container of improved resistance to damage by impact or overheating.

A further object of this invention is to provide a radioactive material shipping container which will continue to retain pressure following subjection to impact and high-temperature conditions.

Still another object of this invention is to provide a radioactive material shipping container of greater capacity.

Still another object of this invention is to provide a radioactive material shipping container of improved gas-retaining ability.

Still another object of this invention is to provide a heat dissipation for a radioactive material shipping container of improved simplicity and reliability.

The above objects, and others, are accomplished in accordance with this invention by providing a radioactive material shipping container having a unique external airflow cooling system, an improved high temperature, high integrity seal on the cask closure head, an arrangement which protects the cask against impact and high-temperature environment, a system for retaining pressure in the cask after an accident and an overall arrangement which provides simple and reliable fuel loading, unloading and shipping.

BRIEF DESCRIPTION OF THE DRAWINGS Details of the invention, and of the preferred embodiment thereof, will be further understood upon reference to the drawings, wherein:

FIG. 1 is an elevation view showing the radioactive material shipping container of this invention installed on a truck for highway transportation with the container also shown in: broken lines in the loading and unloading position;

FIG. 2 is a side elevation view of the container alone;

FIG. 3 is an end elevation view of the container alone;

FIG. 4 is a transverse sectional view through the container taken on line 4-4 in FIG. 2;

FIG. 5 is a longitudinal sectional view through the container taken on line 5-5 in FIG. 4;

FIG. 6 is a transverse sectional view through the container taken on line 6-6 in FIG. 5;

FIG. 7 is a transverse sectional view through the container taken on line 7-7 in FIG. 5;

FIG. 8 is a vertical sectional view through the container head taken on line 8-8 in FIG. 3;

FIG. 9 is a side elevation view of the fuel bundle support basket,

FIG. 10 is an end elevation view of the fuel bundle support basket;

FIG. 11 is a transverse sectional view through the fuel support basket taken on line 11-11 in FIG. 9;

F IG. 12 is a side elevation view of the container assembly including a protective enclosure;

FIG. 13 is a plan view of the container including the protective enclosure;

FIG. 14 is a vertical sectional view through the enclosure taken on line 14-14 in FIG. 12;

FIG. 15 is a side elevation view of the air-cooling duct system only;

FIG. 16 is a side elevation view partly broken away showing the cold weather enclosure;

F IG. 17 is a vertical sectional view through the cold weather enclosure taken on line 17-17 in FIG. 16; and

FIG. 18 is a vertical sectional view through the cold weather enclosure taken on line 18-18 in FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 there is seen a radioactive material shipping container generally designated 10 mounted on a flat deck 11 which is part of a truck and trailer assembly. In the embodiment shown, the deck is supported by a front gooseneck 12 mounted on a conventional tractor I3 and by a rear gooseneck 14. Deck 10 may be disengaged from goosenecks 12 and 14 when desired. For example, the truck may be driven onto a conventional railroad flat car, the deck loweredonto the flat car and secured in place and truck 13 with goosenecks 12 and 14 removed. While container 10 may be mounted on any suitable truck or railroad car, that shown in FIG. 1 is especially preferred because of its adaptability and ability to carry the very heavy container 10.

While in transit, container 10 is covered with an enclosure which may consist of relatively open mesh or a weatherproof cover. These enclosures are described in detail below. These enclosures protect the container from minor impacts, and protect personnel from contact with the hot container.

Container It) is pivoted near its lower end about a pivot 16 mounted on supports 17. In the horizontal, transit, position the upper end of container 10 is supported by projections 19 which rest on pads 20 and are secured thereto.

Container 10 is removed from the transporter by engaging a conventional-crane yoke-with lugs 21 and lifting the container so that it pivots about pivot 16 to the vertical position shown in broken lines in FIG. 1. Crane 18 may then lift container 10 up and away to a suitable location for the removal of head 23 and the loading or unloading of fuel assemblies into the container body.

A pair of blowers 25 are located on the forward part of deck 11. Each blower is driven by an independent engine 27. Air from blowers 25 enters an upper and a lower duct system from which air is directed against the surface of container 10. The lower duct system is included inside deck 11, as is seen in FIGS. 12-15, described below. The upper duct system is secured within the removable protective enclosures shown in FIGS. 12-18, described below. Air from blowers 25 passes through duct 28 into the upper duct system when the outer enclosure is in place.

As best seen in FIGS. 2 and 3, the external surface of the container 10, including head 23, is covered with closely spaced heat transfer fins 29. Preferably, fins 29 are more closely spaced near the middle of the container than adjacent the ends, since heat generation in the radioactive material within container 10 is greatest near the middle of the container and the end portions have greater relative heat transfer surface areas. Valve covers or cupolas 30 and 31 project outwardly from the surface of container 10. The valve covers contain the pressure relief and drain valves, as further described below. The fins on head 23 and the other end of container 29 are preferably of relatively heavy construction to absorb energy in the event of impact on the container and to limit forces transmitted to the cask body. Likewise, cupolas 30 and 31 protecting the pressure relief, vent and drain valves are of sturdy construction and are covered with energy absorbing fins. Upon impact, these fins will deform at a given stress level over a given distance to absorb the energy resulting from the impact.

As seen in FIG. 2, the sides of container 10 are each provided with a pivot lug 33 which engages pivot 16 on support 17 during loading of the container onto the transport vehicle. As the container 10 is swung down into place, support projections 19 and 34 engage pads 20 on deck 11. These pads 20 are shown in broken lines in FIG. 3. As can be seen in FIG. 3, the support surfaces on projections 19 and 34 are tapered slightly to engage detents in the upper surfaces of pads 20. Projections 19 and 34 are then secured to pads 20 by any suitable means, such as the padlock and locking pin means 35 schematically indicated in broken lines in FIG. 3.

When it is desired to remove container 10 from deck 11, latch means 35 are disengaged. Then a conventional crane yoke is brought into engagement with lugs 21. Guide bars 37 are provided to guide the crane frame into engagement with lugs 21. Guide Container 10 is swung into a vertical position and then lifted away with pivot lug 33 automatically disengaging from pivot 16. The container 10 is then taken to the location for loading or unloading the radioactive contents. A plurality of bolts 38 secure head 23 to the body of container 10. These bolts are removed, the head is lifted off and loading or unloading is accomplished in a conventional manner.

Details of the internal construction of container 10 are further pointed out in FIGS. 4 through 8.

FIG. 4 shows a sectional view taken on line 4-4 in FIG. 2. This is essentially the end view of the body of container 10 with head 23 removed. A circle of tapped holes 40 are provided in an inwardly projecting flange 41 for engagement with studs or bolts holding head 23 to the body of the container. An open passageway, having a generally square cross section, extends the length of the body of container 10. This passage is lined with a corrosion-resistant material, such as stainless steel. The space between this liner 43 and the outer wall of container 10 is filled with a shielding material, such as lead. Drain and vent valves 45 and 46 are enclosed within valve covers 30 and 31. These valves are connected by conduits which extend through liner 43 into the internal passageway.

Each end of valve covers 30 and 31 is closed by an access flap 49. The cask is filled with deionized water after the radioactive material is placed therein. Additional water may be introduced, if necessary, through valve 45 or 56. If it is desired that water be drained from the cask, both valves 45 and 46 are opened and air underpressure is introduced through valve 65 and conduit 4l7, forcing water out through conduit 48 and valve 66. Conduit 48 is arranged so that the cask may be entirely drained while in either the vertical or horizontal position. However, water cannot accidentally leak through conduits 47 and 4 8 during transit, since both extend above the water level when container is in the horizontal position and substantial air pressure through conduit 4l7 would be required to force water out through conduit 48.

A pressure relief valve 50 is provided within valve cover 30, connected to conduit 47. In the event of a severe increase in internal pressure within container 10, as could occur should the container by subjected to fire for an extended period in a highway or railroad accident, pressure relief valve 50 will vent the container to prevent rupture of the container. When internal pressure decreases, valve 50 will reclose. If desired, to absolutely prevent leakage through valve 50 during normal operation, a failure-type relief means, such as a rupture disk, may be placed in the line between valve 50 and conduit 47.

Openings 511 are provided, as seen in FIG. 7, for the insertion of thermocouples to monitor the temperature within container l0.

lntemal details of head 23 are shown in FIG. 8. The outer shell of head 23 consists of a corrosion-resistant material such as stainless steel. Within this outer shell is a quantity of a shielding material such as lead. At least one step 53 is provided for engagement with the body of container 10. This step 53 will prevent transverse movement of head 23 with respect to the body of container 10 in the event of the severe impact against any part of container ill). The stepped flanges carry the loads imposed by impact without overstressing the gasket and without permitting skewing or other deformation of the gasket surface which could result in a loss of pressure in the cask. A high integrity seal 56 is provided between head 23 and the body of container 10. Typical gasket seals which would be suitable in this application include Conoseal" gaskets, Spirotalic" gaskets, and metallic 0 rings. Holes 55 areprovided through head 23 for the passage of bolts or studs 38 which secure head 23 to the body of container 10.

FIGS. 9 through llll show a typical basket suitable for supporting irradiated fuel assemblies within the internal passage in container 10. Basket 57 has a generally egg-crate type of cross section, as seen in FIG. 11. The basket shown is capable of supporting 9 fuel assemblies. This basket can, of course, be modified to support more or fewer, smaller or larger diameter, fuel assemblies. A plurality of holes 58 through the basket permit free circulation of liquid within the internal passage. End plate 59 has a plurality of holes 62 to receive the outlet orifices of the fuel assemblies supported in the basket. A typical fuel assembly is indicated in FIGS. 9 and 11 by broken lines 61.

The relatively open protective enclosure, together with the air-cooling duct system, is shown in FIGS. 12 through 15. This wann weather enclosure is made-up of wire mesh or expanded metal, preferably aluminum to save weight. This will serve to protect container 10, and support the duct system while permitting free air circulation. Thus, even if the air-cooling system should fail convection currents will continue to cool the container to a significant degree.

Enclosure 70 consists primarily of a rectangular frame supporting the metal mesh. The upper longitudinal corners of enclosure 70 support the upper ducts 71. When enclosure 70 is put in position, a connecting duct 73 engages with outlet duct 26 on the outlet plenum 74 of blowers 25. Thus, air is conveyed to upper ducts H from which it passes through a plurality of nozzles 76 into impinging contact with container 10. If desired, longitudinal slit nozzles in upper duct 71 with the slot major axis parallel to container 10 may be used in place of the plural nozzles 76. Directing streams of air into forceful contact with the container surface has been found to provide much superior heat removal compared to merely flowing the air along the surface of container 110.

Outlet plenum 74 also connects to a pair of lower ducts 78 as best seen in FIG. 14!. A plurality of nozzles 79 direct air from lower duct 78 into forceful impinging contact with container 10. If desired, longitudinal slot nozzles in lower duct 78 with the slot major axis parallel to container 110 may be used in place of plural nozzles 79. The duct system arrangement is most clearly illustrated in FIG. 15, which shows the duct system standing alone.

A pair of blowers 25 each with its own engine 27 are provided so that if one engine should become inoperative an adequate flow of air through'nozzles 76 and 79 may be maintained. Any suitable blower driving engines may be used, such as gasoline or diesel driven engines. Both blowers discharge into outlet plenum 74l. A nonbackflow damper is provided for each blower so that if one blower is inoperative air will not flow back through it.

FIGS. 16 through 18 show an alternative enclosure for container 10 which is especially suitable for cold weather" use. This enclosure 81 is generally rectangular in configuration and consists of panels, such as galvanized steel or aluminum sheets. Thermal insulation 82 may be provided as desired. Thermostatically controlled louvers 83 are provided on each side of enclosure 811 adjacent the center of container 10. These louvers will ordinarily be closed at low temperatures and will open automatically when the temperature within enclosure 81 rises to the point where blowers 25 are turned on to cool container 10. Fixed louvers 84 are provided adjacent the inlet to blowers 25 so that air will be supplied to the blowers at any time. Thermostatically controlled louvers 85 are also provided on the end wall dividing the end of container 10 from the air inlet section for blowers 25.

Enclosure fill carries an upper duct system 86 identical with that carried by the warm weather enclosure 70.

Any other suitable enclosure and ducting system may be used if desired. However, it is important that the airstrearns be directed into forceful impinging contact with the heat transfer surfaces on container 10. The enclosures and ducting system described above are preferred for use with the radioactive materials container and cooling system of this invention Although specific materials and arrangements have been described in the above description of a preferred embodiment, other suitable materials and conditions, as indicated above, may be used with similar results. Other modifications and applications of the present invention will occur to those skilled in the art upon reading this disclosure. These are intended to be included within the scope of this invention.

ICLAIM:

l. A system for transporting radioactive material, comprismg: a container for said radioactive material including an elongated hollow body having an internal passage, a removable closure for said passage, a radiation shield surrounding said passage, a support within said passage adapted to receive said material; a plurality of spaced fins projecting from the external surface of said body, a transport deck including means for removably receiving and securing said container thereto; means forming a source of pressurized air; a first system of ducts supported by said deck and receiving pressurized air from said source; a removable protective enclosure surrounding said container above said deck; a second system of ducts supported by said enclosure and adapted for removable connection to said source for receiving pressurized air therefrom; and a plurality of nozzles connected to said ducts for receiving pressurized air therefrom and for directing high velocity airstreams onto the external surfaces of said container.

2. The system of claim 1 wherein said means for removably receiving and securing said container to said deck includes pivoting means adapted to permit movement of said container between a horizontal and a vertical position while being supported by said deck. 

1. A system for transporting radioactive material, comprising: a container for said radioactive material including an elongated hollow body having an internal passage, a removable closure for said passage, a radiation shield surrounding said passage, a support within said passage adapted to receive said material; a plurality of spaced fins projecting from the external surface of said body, a transport deck including means for removably receiving and securing said container thereto; means forming a source of pressurized air; a first system of ducts supported by said deck and receiving pressurized air from said source; a removable protective enclosure surrounding said container above said deck; a second system of ducts supported by said enclosure and adapted for removable connection to said source for receiving pressurized air therefrom; and a plurality of nozzles connected to said ducts for receiving pressurized air therefrom and for directing high velocity airstreams onto the external surfaces of said container.
 2. The system of claim 1 wherein said means for removably receiving and securing said container to said deck includes pivoting means adapted to permit movement of said container between a horizontal and a vertical position while being supported by said deck. 